refactor: remove legacy strategy bridge

[Pigbibi]

Summary

• migrate IB mainline execution to unified strategy runtime plus decision mapper
• remove the legacy signal-module bridge after moving required metadata to unified adapters
• add runtime and mapper regression tests while leaving unrelated research files untouched

Test Plan

• python3 -m py_compile main.py strategy_loader.py strategy_runtime.py tests/test_strategy_loader.py tests/test_strategy_runtime.py
• python3 -m ruff check main.py strategy_loader.py strategy_runtime.py tests/test_strategy_loader.py tests/test_strategy_runtime.py
• PYTHONPATH=.:/Users/lisiyi/Projects/QuantPlatformKit/src:/Users/lisiyi/Projects/UsEquityStrategies/src ./.venv/bin/python -m pytest tests/test_strategy_loader.py tests/test_strategy_runtime.py tests/test_decision_mapper.py tests/test_rebalance_service.py tests/test_request_handling.py tests/test_runtime_config_support.py tests/test_snapshot_strategy_runtime.py -q